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Improve RangeDelAggregator documentation

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Summary:
as requested in D62259
Closes https://github.com/facebook/rocksdb/pull/1434

Differential Revision: D4099047

Pulled By: ajkr

fbshipit-source-id: a258cfb
This commit is contained in:
Andrew Kryczka 2016-10-28 15:44:48 -07:00 committed by Facebook Github Bot
parent 0a9fd05c2a
commit 2946cadc46
1 changed files with 37 additions and 2 deletions
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39
db/range_del_aggregator.h
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@ -20,17 +20,52 @@
#include "util/kv_map.h"
namespace rocksdb {
// A RangeDelAggregator aggregates range deletion tombstones as they are
// encountered in memtables/SST files. It provides methods that check whether a
// key is covered by range tombstones or write the relevant tombstones to a new
// SST file.
class RangeDelAggregator {
public:
// @param snapshots These are used to organize the tombstones into snapshot
// stripes, which is the seqnum range between consecutive snapshots,
// including the higher snapshot and excluding the lower one. Currently,
// this is used by ShouldDelete() to prevent deletion of keys that are
// covered by range tombstones in other snapshot stripes. In case of writes
// (flush/compaction), all DB snapshots are provided such that no keys are
// removed that are uncovered according to any DB snapshot. In case of read
// (get/iterator), only the user snapshot is provided such that the seqnum
// space is divided into two stripes, where only tombstones in the older
// stripe are considered by ShouldDelete().
RangeDelAggregator(const InternalKeyComparator& icmp,
const std::vector<SequenceNumber>& snapshots);
// Returns whether the key should be deleted, which is the case when it is
// covered by a range tombstone residing in the same snapshot stripe.
bool ShouldDelete(const Slice& internal_key, bool for_compaction = false);
bool ShouldAddTombstones(bool bottommost_level = false);
// Adds tombstones to the tombstone aggregation structure maintained by this
// object.
// @return non-OK status if any of the tombstone keys are corrupted.
Status AddTombstones(ScopedArenaIterator input);
Status AddTombstones(std::unique_ptr<InternalIterator> input);
// write tombstones covering a range to a table builder
// usually don't add to a max-level table builder
// Writes tombstones covering a range to a table builder.
// @param extend_before_min_key If true, the range of tombstones to be added
// to the TableBuilder starts from the beginning of the key-range;
// otherwise, it starts from meta->smallest.
// @param next_table_min_key If nullptr, the range of tombstones to be added
// to the TableBuilder ends at the end of the key-range; otherwise, it
// ends at next_table_min_key.
// @param meta The file's metadata. We modify the begin and end keys according
// to the range tombstones added to this file such that the read path does
// not miss range tombstones that cover gaps before/after/between files in
// a level.
// @param bottommost_level If true, we will filter out any tombstones
// belonging to the oldest snapshot stripe, because all keys potentially
// covered by this tombstone are guaranteed to have been deleted by
// compaction.
void AddToBuilder(TableBuilder* builder, bool extend_before_min_key,
const Slice* next_table_min_key, FileMetaData* meta,
bool bottommost_level = false);